In general, rotating wheel type or mechanical type gyroscopes have been used for many years as gyroscopes. However, gyroscopes of this type have had problems in that component costs are high because of extremely high requirements on accuracy of their shapes and in that their durability is insufficient because of the presence of mechanically sliding sections.
In order to solve the above problems, optical gyroscopes having a configuration for optically detecting attitude changes have been proposed. An optical gyroscope normally takes advantage of the Sagnac effect that is a phase difference generated between two light waves propagated in a closed optical loop in directions opposite to each other, the phase difference being proportionate to the rotation. Referring to types of optical gyroscopes, there is an interference type in which interference between two light waves is measured as described above, a resonance type in which an optical ring resonator having high fineness is configured to measure changes in an optical resonance frequency attributable to the Sagnac effect, and a ring laser type in which a laser is configured using simulated Brillouin scattered light that is generated in a fiber by incident light having high power.
Various optical gyroscopes have been proposed, including those which use a gas laser, a semiconductor laser or a light-emitting diode as a light source depending on the materials of which they are made up and those which use an optical resonator or optical fiber to form an optical loop.
Referring to specific examples of the prior art, for example, Japanese Patent Publication No. 27194/1996 has disclosed an interference type optical fiber gyroscope having a detection coil constituted by an optical fiber. Japanese Patent Laid-Open No. 288556/1993 has disclosed a semiconductor laser gyro in which a ring resonator is formed on a semiconductor substrate having a p-n junction; laser oscillation is caused by injecting a carrier from an electrode in an overlapping relationship with the ring resonator; and interference signal between two light waves emitted by the ring resonator is detected by an electrode that is provided separately.
However, in the case of an interference type gyroscope such as the optical fiber gyroscope disclosed on the above-cited Japanese Patent Publication No. 27194/1996, since it must have a great optical path length (which may range from several meters to several kilometers), a problem arises in that a detecting section has great dimensions even if an optical fiber is used. In particular, an optical fiber occupies a considerably great volume as a whole because it has protective layers called clads formed around a core that constitutes a light guide path. Therefore, it is very difficult to form with small dimensions suitable for applications including use in vehicles or portable apparatus.
In the case of an apparatus having a ring resonator such as the semiconductor laser gyro disclosed in the above-cited Japanese Patent Laid-Open No. 288556/1993, there is a problem in that frequency locking referred to as lock-in occurs at a low angular velocity to disable detection of rotation.
The invention solves the above-described problems, and it is an object of the invention to provide an optical gyroscope that is smaller than those in the prior art. There is also provided a compact optical gyroscope capable of detection at a low angular velocity without any problem.